All-optical multi-casting permits the establishment of high-quality, high-bandwidth point-to-multipoint applications in metropolitan area networks by diffusing an incoming data carrying wavelength onto a number of outgoing wavelengths. With the proliferation of hybrid Wavelength Division Multiplex (WDM)/Optical Time Division Multiplex (OTDM) networks, the ability to perform high-speed broadcasting of OTDM signals at multiple wavelengths will prove an efficient method in the dissemination of information over WDM. Current approaches to WDM multi-casting involve the execution of multiple cycles of optical-electronic-optical conversion, thus necessitating the use of costly high-speed electronics and optoelectronics. All-optical multi-casting would therefore remove such constraints while concurrently providing for a higher level of network transparency thereby improving network management and performance. To date, the issue has most promisingly been addressed through the manipulation of nonlinear phenomena within semiconductor optical amplifiers (SOA). The demonstrations so far however, have exhibited either low conversion efficiency or operating speed constraint or a complicated setup. All-optical Mach-Zehnder interferometer (MZI) approaches are therefore particularly attractive as they are not limited by the aforementioned constraints, while still offering a low switching power requirement at high-speed and a high level of integratability. In this paper we present a detailed model replicating a 40Gb/s experimental setup in order to investigate the operational limit of the MZI when employed in WDM multi-casting. Through simulation we examine the factors determining the constraints imposed on the maximum number of output multi-cast channels that can be achieved using such a device and establish its suitability as a next-generation all-optical multi-caster.